1. Field of the Invention
The present invention relates to a zoom lens and an image pickup apparatus including the same, which are suitable for, for example, a broadcasting television camera; a video camera, a digital still camera, a surveillance camera, and a silver halide film camera.
2. Description of the Related Art
In recent years, a zoom lens having a wider angle of view, a high zoom ratio, and high optical performance is required for an image pickup apparatus such as a television camera, a silver halide film camera, a digital camera, or a video camera. As a zoom lens having a wider angle of view and a high zoom ratio, a positive lead type five-unit zoom lens constituted of five lens units including a positive lens unit disposed closest to the object side is known.
As this positive lead type zoom lens, a five-unit zoom lens in which three movable lens units including a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power perform magnification-varying and correction of image plane variation due to the magnification-varying is known (Japanese Patent Application Laid-open Nos. H07-248449, 2009-128491, and 2009-128492).
Japanese Patent Application Laid-open No. H07-248449 discloses a zoom lens having a zoom ratio of approximately 17 and a photographing field angle of approximately 70 degrees at a wide-angle end. Japanese Patent Application Laid-Open Nos. 2009-128491 and 2009-128492 disclose a zoom lens having a zoom ratio of approximately 54 and a photographing field angle of approximately 60 degrees at the wide-angle end.
In order to obtain high optical performance while maintaining a wider angle of view and a higher zoom ratio in the five-unit zoom lens, it is important to appropriately set a refractive power arrangement, a configuration, and the like of each lens unit. In particular, it is important to appropriately set movement conditions during zooming of the second, third, and fourth lens units serving as magnification-varying lens units, the refractive power of the first lens unit, and the like. Other than that, it is important to appropriately set a combined refractive power of the third and fourth lens units, moving loci of the third and fourth lens units from the wide-angle end to an intermediate zoom position, and the like. If these configurations are not appropriately set, it becomes difficult to provide a zoom lens having a wide angle of view, a high zoom ratio, and high optical performance over an entire zoom range.
In the zoom lenses disclosed in Japanese Patent Application Laid-open Nos. H07-248449, 2009-128491, and 2009-128492, the refractive powers and the moving loci of the magnification-varying lens units are defined so that an imaging magnification of a combined lens unit constituted of the third and fourth lens units is always −1 when an imaging magnification of the second lens unit is −1 at a predetermined intermediate zoom position. In order to achieve such high zoom ratio of the zoom lens, effective diameters of the third and fourth lens units are apt to foe increased so that variations of aberrations due to Booming are increased. The high zoom ratio means a zoom ratio of approximately 20 to 35 when the angle of view is approximately 75 to 85 degrees at the wide-angle end or a zoom ratio of approximately 80 to 130 when the angle of view is 60 to 67 degrees at the wide-angle end. In addition, there is a tendency that an increase in mass due to the increase in the effective diameter causes difficulty in securing higher speed of zoom action and quick response to zoom operation.